The spectral decomposition of \(\)  is \(=\Lambda ^{-1}\) 
where the eigenvectors of \(\)  form the columns of matrix \(\)  [1]}. We note that \(^{-1} = ^T\)  if \(\)  is symmetric, that is, the graph \(G\)  is undirected. \(\Lambda \in ^{N\times N}\)  is the diagonal matrix of corresponding
ordered eigenvalues \(\lambda _0, \, \ldots , \, \lambda _{N-1}\)  of \(\) . These eigenvalues represent frequencies on the graph [2]}.
